1. Field of the Invention
This invention relates to laser gyrometers for the determination of the angular speed of a rotating system by measuring the phase-shift between two coherent light beams, guided in a wound optical fibre, in the direction of the rotation, and in the opposite direction respectively.
2. Description of the Prior Art
Such gyrometers generally make an interferometric measurement of the phase-shift, the beams emerging from the two ends of the fibre being recombined, which established and interference state depending upon the angular speed of the system. A quadratic detector collecting this beam supplies an electric signal characteristic of the luminous intensity which is directly related to the phase-shift and hence to the angular speed.
In order to obtain a linear relation between the detected intensity and the phase-shift, a fixed phase-shift of .pi./2 is introduced between the two waves. Such a phase-shift is difficult to obtain. Furthermore, the phase-shift related to the rotation is weak and any asymmetry in the arrangement produces parasitic phase-shift of which the thermally or mechanically induces fluctuations create considerable additional noise which gives rise to a loss of sensitivity in the speed measurement. The two light beams intended to enter the two ends of the fibre are obtained by the separation of a single beam issuing from the a laser. The separation and subsequent recombination, after propagation in the fibre, of these two beams is generally obtained by means of a semi-transparent plate of which the transmission and reflection factors are carefully selected.